Jonathan witnesses a murder. In his rush to approach the scene of the crime, he is hit by someone on a mo-ped. The blow to his head causes temporary amnesia and the killer must get rid of Jonathan before his memory returns.

Jennifer is mistaken for her look-alike, Dominique, and is kidnapped by ruthless killers. With the help of an unscrupulous columnist, the police, and the real Dominique, Jonathan devises his plan to save Jennifer.

Normally finicky, Freeway is quite fond of a new dog food and ends up in a dog food commercial. When the Harts have a party, some of Freeway's new food is mistakenly ingested by some guests who then behave as if drugged. Jennifer and Jonathan are in danger when they attempt to find out its secret formula.

Industrial espionage is a problem at Hartoy company. When the investigator Jonathan has hired is murdered, the Harts go undercover in an attempt to foil the crooks and save the company from financial destruction.

During an Opening Night party for a new Egytian exhibit at the museum, the man who discovered the tomb is murdered. The Harts become involved in the investigation when Jennifer sees a mummy at their home

At a croquet game in Hawaii, a player is stabbed and dies at Jonathan's feet, muttering something about a key. Two of the spectators suddenly become interested in the Harts.

Max's ex-wife, presumed dead for over 10 years, arrives in Los Angeles. Her friend is murdered, so she calls Max for help. When two thugs try to grab her at the park, she is injured and Max is kidnapped. Demands are made for a necklace about which the Harts know nothing.

At the opera, Jonathan is mistaken for a hitman and is given an envelope containing $100,000 for the job. When the messenger is murdered, Jonathan poses as the hitman in an attempt to save the victims life.

Jennifer orders three chocolate valentines. Someone makes a mistake and delivers the wrong heart for the Harts. One contains a smuggled object that the thieves want at any cost.

Chief accountant of Hart Industries, Stanley Friesen, is set up to take a murder wrap after an evening on the town. In an attempt to clear him, the Harts retrace his steps and discover a gambling ring using the Nightlife as a cover.

To strip mine the entire area, a ruthless mining tycoon is driving cattle ranchers out of business by poisoning the livestock via the stream that waters the properties. The Harts get involved when Jennifer's colt is poisoned.

An employee delivers some papers to Jonathan, along with evidence of a murder. She hides the clue in Freeway's toy and the Harts are held hostage by the murderer.

Vince, a friend of Max's, arrives in USA to open a chain of health clubs. International criminals smuggle a solid gold barbell into the country with Vince's entourage.

Jonathan and Jennifer set sail, incognito, on a gambling ship in an attempt to crack a counterfeiting ring.

The Harts' unscrupulous lawyer hires an assassin to eliminate Jonathan with plans to court and marry Jennifer and thus gain control of the sizeable estate.

Jennifer's article on the world of high fashion leads to Jonathan and Jennifer modeling for a famous photograper while trying to determine who is murdering beautiful models.

Jennifer, flying a kite in the park, falls and hits her head. She's hospitalized with a slight concussion. While in hospital, she witnesses the murder of another patient and tries to convince Jonathan of the strange crime is being covered up.

Jennifer's death scene in an amatuer production could become the real thing when the director realizes she can identify him as a murderer of a young playwright.

The Harts return home and find their house ransacked. During the clean-up, they discover a hidden hallway and vault. The Harts and their friend Ida are sealed in the vault when the crooks return to claim the municipal bonds hidden in the vault.